1. Field of the Invention
The present invention relates generally to internal combustion engines and, more particularly, is concerned with hydraulic operating system for opening and closing a valve of an internal combustion engine.
2. Description of the Prior Art
Mechanical mechanisms by which the valves of an internal combustion engine are operated to take air or a fuel-air mixture into the cylinders of the engine and discharge the products of combustion from the cylinders are well known. In most four-stroke engines, the valve is of the inwardly-opening poppet type with its head being held against a seat in the cylinder head when the valve is closed and displaced toward the engine piston within the cylinder when the valve is opened.
Typically, the mechanical mechanism for operating each valve includes a camshaft driven off the engine crankshaft and having a cam thereon matched with each valve. Also, a linkage of the mechanism composed of a cam follower, push rod and rocker arm is associated with each cam for translating its rotary motion to reciprocatory motion to drive the corresponding valve between closed and opened conditions. In addition, a compressed helical spring is provided surrounding and engaged with the end of the valve opposite to its head for biasing the valve toward its seat.
After the cam accelerates the valve via the linkage toward the piston, the spring must be capable of decelerating the valve and then return it to the closed seated condition. In order to accomplish this, each spring must be strong enough to overcome the inertia of the linkage and the valve as well as to hold the cam follower on the cam at all times when running the engine at high speed. At such speed and load, the proportion of total engine output used to compress the spring is small. However, when running the engine at low speed with low load, the proportion of the total engine output used just to compress the spring is significantly higher. This requirement of conventional mechanical valve-operating mechanisms constitutes a major obstacle to improvement of fuel economy at engine idle and cruise speed and load conditions.
Consequently, a need exists for a fresh approach to operation of internal combustion engine valves which will avoid the aforementioned obstacle, without introducing a new one in its place, and will lead to improved fuel economy.